In the current version of the Fitnet App, the camera of an exerciser's smartphone captures data from him (upper left), while a prerecorded trainer guides him through a workout. A clock (bottom center) shows elapsed time. The orange dots (upper left) indicate he's following her routine well, as judged by the camera and phone's app. The app can also estimate the exerciser's number of steps. Courtesy of FitNet hide caption

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Even golfers using a motorized cart can burn about 1,300 calories and walk 2 miles when playing 18 holes. Halfdark/fstop/Corbis hide caption

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Yoga practitioners celebrate the solstice in New York's Times Square in 2011. Richard Drew/AP hide caption

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In a FIT zone at Bell Street Park in East Palo Alto, Calif., friends from the neighborhood now gather regularly to play volleyball. Jeremy Raff/KQED hide caption

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NPR senior Washington editor Beth Donovan walks on a treadmill desk in her office in Washington, D.C. Meredith Rizzo/NPR hide caption

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Olympic gold medalist Sanya Richards-Ross pulls on compression sleeves before a 400-meter race at the World Indoor Athletics Championships in Istanbul in 2012. Martin Meissner/AP hide caption

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Greg O'Brien gathers his thoughts before a run in 2013. "Running is essential," he says. Michael Strong/Living With Alzheimers hide caption

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Coss Marte started selling drugs at age 13 and by 19, he says, he was making $2 million a year. After serving a prison sentence, he founded a "prison style" fitness boot camp. Justin Fennert/Courtesy of Behind the Stache hide caption

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Joyce Powell, 80, attends an exercise class at UT-Arlington with her husband, Thomas (right). Powell says she feels more confident in getting around and traveling since taking the classes. Dane Walters/KERA hide caption

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Varying speed while walking may make the activity much more effective. iStockphoto hide caption

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Dr. Robert Zarr, second from right, leads a hike through a park in Washington, D.C. Diana Bowen/National Park Service hide caption

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